1. Technical Field
The present invention is based upon work supported by the National Science Foundation under NSF Grant DMR 81-03100.
The present invention is concerned with new organic compounds which are particularly suitable as photoinitiators. The present invention is especially concerned with peresters. The peresters of the present invention are especially useful as photoinitiators for the polymerization of ethylenically unsaturated materials.
2. Background Art
Photoinitiators are free-radical sources which decompose photochemically and are employed especially as initiators in the polymerization of ethylenically unsaturated materials. In view of the efficient control photoinitiated polymerization offers, such as assumed great importance in recent years in the printing and electronics industries such as in printing inks, paints and photoresist coatings.
Among typical commercial initiators are three general types: mixtures of aryl ketones, benzoin ethers, or substituted acetophenones. In past years, highly halogenated aryl hydrocarbons were also used for initiators, but their use is now precluded because they are so highly toxic.
Among the more important commercially used photoinitiators for acrylate polymerization is the so-called "Hammond initiator", benzophenone-Michler's ketone.
A major advantage of the Hammond initiator is the rate by which it initiates radical chain reactions; two important disadvantages are the rather large amount of initiator needed to make the rate of polymerization sufficiently rapid for printing applications and the potential toxicity of one of the initiator partners--Michler's ketone (4,4'-bis(N,N-dimethylamino)benzophenone).
To be of real practical significance as a photoinitiator, a compound must be relatively thermally stable but must also be labile when irradiated with wavelengths of UV or visible light. Accordingly, providing new compounds which possess this combination of properties is quite difficult. For instance, various benzophenone derivatives of benzoyl peroxide have been studied. For example, see Leffler et al; Journal American Chemical Society, 1971, 93, 7005 et seq. However, such derivatives are not especially stable thermally. It has also been noted that the photochemical efficiency of triplet benzophenone sensitized decompositions of peroxides in solution is low (e.g.--see Walling et al., Journal Americal Chemical Society, 1965, 87, 3413 et seq.).